COMPLETE SEQUENCE OF A RHIZOBIUM PLASMID CARRYING GENES NECESSARY FORSYMBIOTIC ASSOCIATION WITH THE PLANT HOST

The soil bacteria rhizobia have the capacity to establish nitrogen-fix ing symbiosis with their leguminous host plants. In most Rhizobium spe cies the genes for nodule development and nitrogen fixation have been localized on large indigenous plasmids that are transmissible, allowin g lateral transfer of symbiotic functions. A recent paper reports on t he complete sequencing of the symbiotic plasmid pNGR234a from Rhizobiu m species NGR234((1)), revealing not only putative new symbiotic genes but also possible mechanisms for evolution and lateral dispersal of s ymbiotic nitrogen-fixing abilities among rhizobia.